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Thu, 9 Jul 2026 21:56:51 +0000 (GMT) From: Shrikanth Hegde To: linux-kernel@vger.kernel.org, mingo@kernel.org, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, yury.norov@gmail.com, kprateek.nayak@amd.com, iii@linux.ibm.com, corbet@lwn.net Cc: sshegde@linux.ibm.com, tglx@kernel.org, gregkh@linuxfoundation.org, pbonzini@redhat.com, seanjc@google.com, vschneid@redhat.com, huschle@linux.ibm.com, rostedt@goodmis.org, dietmar.eggemann@arm.com, maddy@linux.ibm.com, srikar@linux.ibm.com, hdanton@sina.com, chleroy@kernel.org, vineeth@bitbyteword.org, frederic@kernel.org, arighi@nvidia.com, pauld@redhat.com, christian.loehle@arm.com, tj@kernel.org, tommaso.cucinotta@gmail.com, maz@kernel.org, rafael@kernel.org, rdunlap@infradead.org, kernellwp@gmail.com, linux-doc@vger.kernel.org Subject: [PATCH v7 00/12] sched, steal_monitor: Introduce cpu_preferred_mask and steal-driven vCPU backoff Date: Fri, 10 Jul 2026 03:26:36 +0530 Message-ID: <20260709215648.1246821-1-sshegde@linux.ibm.com> X-Mailer: git-send-email 2.54.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; 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It is denoted as cpu_preferred_mask - Periodically compute the steal time. If steal time is high/low based on the thresholds, either reduce/increase the preferred CPUs. This is handled in a new driver called steal_monitor - If a CPU is marked as non-preferred, push the task running on it if possible. - Use this CPU state in wakeup and load balance to ensure tasks run within preferred CPUs. For more details on idea, problem statement and performance numbers, please refer to cover-letter of v2[2] and OSPM talk[1]. *** Please review and provide your feedback!! *** [1]:https://youtu.be/adxUKFPlOp0 [2] v2: https://lore.kernel.org/all/20260407191950.643549-1-sshegde@linux.ibm.com/#t [3] v6: https://lore.kernel.org/all/20260701141654.500125-1-sshegde@linux.ibm.com/#t Thank you very much for feedback so far. This has helped the code to evolve towards a clear abstraction layers and get simplified. Special thanks to Yury Norov for reviewing this and improving the series significantly. Really appreciated. Apologies in advance if I have missed addressing any comments. If so would be purely accidental, not in any way intentional. base commit: tip/sched/core at 'commit 04998aa54848 ("sched/eevdf: Delayed dequeue task can't preempt")' v6->v7: - Make new driver steal_monitor into 4-5 patches. (Yury Norov) - Define CONFIG_STEAL_MONITOR and Make it select CONFIG_PREFERRED_CPU (Yury Norov) - Make module parameters fixed at module load (Yury Norov) - Make module parameters checks using set/get methods via module_param_cb - sashiko - Simplify is_cpu_allowed. (Yury Norov) - Added MAINTAINERS entry for new driver. - Split nohz_full optimization into its own patch. - Merged load balance patches. - Use possible CPUs instead of active for steal value calculations. - Drop __weak symbol for now. Once the need arises, framework can be designed at that time. (Yury Norov) - remove whitespace in scoped_guard (Yury Norov) - remove class check in sched_push_current_non_preferred_cpu (Yury Norov) - Make empty stub to do { } while (0) in set_cpu_preferred - Move is_migration_disabled check to sched_non_preferred_cpu_push_stop - Sashiko - Increase the migration count only if rq changed - sashiko - Add missing requeue work on early return - sashiko - Use WARN_ON_ONCE for design checks instead of WARN_ON. - Few updates to documentation, comments and changelogs. Let me know if there is any critical information is missing regarding new driver such as policy, documentation or missing implementation. I have ensured checkpatch --strict is happy. Shrikanth Hegde (12): sched/docs: Document cpu_preferred_mask and Preferred CPU concept cpumask: Introduce cpu_preferred_mask sysfs: Add preferred CPU file sched/core: Try to use a preferred CPU in is_cpu_allowed sched/fair: Load balance only among preferred CPUs sched/core: Push current task from non preferred CPU sched/debug: Add migration stats due to non preferred CPUs virt: Introduce steal monitor driver virt/steal_monitor: Add control knobs for handling steal values virt/steal_monitor: Provide functions for managing steal values virt/steal_monitor: Act on steal time periodically and decide on preferred CPUs sched, virt/steal_monitor: Keep tick on for faster push on nohz_full CPU .../ABI/testing/sysfs-devices-system-cpu | 11 + Documentation/driver-api/index.rst | 1 + Documentation/driver-api/steal-monitor.rst | 111 ++++++++++ Documentation/scheduler/sched-arch.rst | 58 +++++ MAINTAINERS | 9 + drivers/base/cpu.c | 8 + drivers/virt/Kconfig | 2 + drivers/virt/Makefile | 1 + drivers/virt/steal_monitor/Kconfig | 18 ++ drivers/virt/steal_monitor/Makefile | 6 + drivers/virt/steal_monitor/defaults.c | 107 ++++++++++ drivers/virt/steal_monitor/sm_core.c | 202 ++++++++++++++++++ drivers/virt/steal_monitor/sm_core.h | 37 ++++ include/linux/cpumask.h | 24 +++ include/linux/sched.h | 1 + kernel/Kconfig.preempt | 3 + kernel/cpu.c | 6 + kernel/sched/core.c | 105 ++++++++- kernel/sched/debug.c | 1 + kernel/sched/fair.c | 11 +- kernel/sched/sched.h | 20 ++ 21 files changed, 737 insertions(+), 5 deletions(-) create mode 100644 Documentation/driver-api/steal-monitor.rst create mode 100644 drivers/virt/steal_monitor/Kconfig create mode 100644 drivers/virt/steal_monitor/Makefile create mode 100644 drivers/virt/steal_monitor/defaults.c create mode 100644 drivers/virt/steal_monitor/sm_core.c create mode 100644 drivers/virt/steal_monitor/sm_core.h -- 2.47.3